1. Field of Invention
The current invention relates generally to apparatus, systems and methods for radio communication. More particularly, the apparatus, systems and methods relate to extracting information from a received signal. Specifically, the apparatus, systems and methods provide for methods and systems for extracting time of arrival (TOA) information from a noisy signal.
2. Description of Related Art
It is desirable to be able to utilize existing radio communication signals, such as those employed in military environments, to perform range estimation. The use of standard communication signals, as opposed to special purpose ranging signals, allows existing radio systems to be outfitted with ranging algorithms, giving the advantage of ranging and navigational support without adding additional equipment to the platform. This permits deployment of the technology on existing platforms without adding size, weight or material costs, a significant value enhancement in crowded equipment bays or in man-carried mobile applications.
In radio communications, there is a delay in propagation between transmitter and receiver nodes in a network. This delay is directly proportional to the distance traveled by the radio wave, including reflections if any. In many scenarios there is a dominant direct path (line of sight) whose length is proportional to the straight line range between nodes. By identifying and measuring this path, particularly the TOA of the signal component it carries, a useful estimate of the range may be obtained.
The accurate estimation of TOA is complicated by several factors that are present in a communications scenario. First, the available signal is data-dependent (encoded with user information). In general, this obscures the waveform structure that is to be exploited in measuring TOA and so the data dependency must be stripped before range estimation is possible. Second, the operating environment generally includes multiple reflectors and scattering media resulting in a received signal that is characterized by multi-path. Third, range (TOA) accuracy depends on the bandwidth of the underlying signal which may be limited. This limitation is particularly important in the use of linear processing techniques since the available precision and resolution is nominally equal to the reciprocal of the signal bandwidth. Since it is desirable to estimate the leading edge of the signal multi-path bundle, it is imperative that the respective “rays” be resolvable. For this reason it becomes necessary to utilize non-linear techniques, such as subspace methods MUSIC, root-MUSIC, and ESPRIT.
A need, therefore, exists for an improved method for extracting TOA from a waveform.